Plaster of paris in ice cube trays. Just put a paper clip or twisty tie in them so you can hang them on something. Big poof of white smoke when you hit them.
That could be interesting. Flour tossed in the air is explosive. I wonder if the bullet would be hot enough to set it off when the flour is dispersed?Baggies or balloons of flour .. Just thought of it a sec ago .. I am gonna try it ..